Hemodialysis is now a commonly practiced method of treating patients suffering from renal failure. Hemodialysis machines serve to remove life-threatening chemicals from the blood stream, when the kidneys can no longer effectively remove such chemicals.
In order to perform hemodialysis, access must be obtained to the blood flow system, and blood flows of 150 to 400 ml/minute are required. Blood from veins is inadequate to meet these flow requirements, and repeated puncture of a large artery is not feasible.
Accordingly, a medical procedure has been developed whereby a fistula is created by surgically anastamosing a superficial artery and a nearby vein. The fistula is a surgical connection of an artery to a vein. When such a connection is created, the blood flow through the blood vessels involved is increased since the flow resistant capillaries are bypassed. The pressure at the venous side of the fistula is also increased, causing the vein to enlarge its diameter and causing the walls of the vein to thicken. Once these changes have taken place, the transformed vein becomes a site with a suitably large diameter and blood flow to puncture with needles for the purpose of connecting the patient to a dialysis machine.
If a native vein is not available for the anastomosis because the patient's blood vessels are not suitable for the formation of a fistula or the patient's blood vessels are not healthy enough for a fistula to be created, an artificial vessel or vascular graft is used to bridge an artery and a nearby vein. The material of the graft is suitable for puncturing with needles to achieve the necessary access to the patient's blood system.
These type of grafts are often connected between the distal radial artery and the cephalic or basilic vein. Each end of the fistula is anastomosed in an end-to-side fashion to the respective artery or vein. The most commonly used material to form prosthetic vascular grafts is expanded polytetrafluoroethylene (PTFE). And cannulation of arteriovenous fistulas or graft fistulas with 14-16 gauge needles permits blood flow sufficient to carry out hemodialysis.
The grafts are implanted entirely below the skin to reduce the risk of infection and to provide better comfort to the patient between dialysis treatments. A hypodermic needle is used to cannulate the vessel through the skin. During cannulation of the graft fistulas, direct punctures of the graft walls are made with the needles. One puncture is made in the graft wall in the arterial side and one puncture is made in the venous side. Repeated punctures of the graft material promote rupture of the graft, pseudoaneurysms, and the development of organized thrombus within the lumen of the graft. Organized thrombus may be the cause of graft thrombosis and eventual graft failure.
Repeated, direct punctures of the graft wall also require compression for hemostasis following the dialysis session. Excessive compression during hemostasis may cause decreased flow within the graft and thrombosis. Also, there is very little subcutaneous tissue between the surface of the skin and the graft wall reducing the capacity of extra luminal coagulation of the blood within the surrounding tissue and therefore causing reduced hemostasis at the end of the procedure.
What is needed is a dialysis access graft fistula that better provides for repeated cannulation while reducing the occurrence of ruptures of the graft, pseudoaneurysms, and the development of organized thrombus; and that reduces the problems discussed above with hemostasis.